The present invention relates to a high availability network device and more specifically to a redundant control plane architecture for use in a network switch or router.
In recent years telecommunications and data networks have become pervasive in industry and commerce. In a telecommunications or data network, information is conveyed from one user or application to another user or application through the network via a series of interconnected network switches or routers. Forwarding tables stored within each switch or router determine the output port to which received traffic should be forwarded.
Typically, network devices such as network switches or routers include line cards that have input and output ports coupled to corresponding communication links. The line cards are also communicably coupled to a switch fabric. Data units received at an input port are forwarded to the switch fabric and to at least one ouput port of at least one line card for forwarding over the associated communication link. The selection of the appropriate output port or ports for data unit forwarding is determined by reference to the forwarding tables.
There is an ongoing need during the operation of a network device to update the forwarding tables and otherwise convey control and configuration information to line cards that are responsible for data receipt and forwarding. Typically, forwarding tables are updated “inband” with the payload data being conveyed by the network device. The transmission of forwarding tables, control and configuration information inband undesirably occupies bandwidth that might otherwise be available for data traffic.
Moreover, it is generally important for the network device to have high availability since the failure of a network switch or router can result in the loss of critical data. The loss of the ability to update forwarding tables or otherwise modify the control and configuration information within line cards of the network device typically renders the network device unusable. Additionally, the failure of a component within the control path for a network device can lead to costly unscheduled maintenance.
For these reasons, it would be desirable for a network switch or router to include a fault tolerant control plane that includes the capability to redirect forwarding tables, control and configuration information through an alternative control path in the event a failure is detected in the active control path.